In January 2022, Hahn moved over to the primary NXT brand in America, where his ring name was changed to Gunther, before being promoted to the main roster on SmackDown in April that year.

After moving to the Raw brand in 2023, he went on to win the King of the Ring tournament and won the World Heavyweight Championship at SummerSlam in August 2024.

Raaber reached out to Pro Wrestling ZERO1-MAX, the founded promotion of Shinya Hashimoto and Shinjiro Otani, and asked if Hahn could train with ZERO1-MAX and its heavyweight trainers, which consisted of Riki Choshu and his protege Tomohiro Ishii, and Tatsuhito Takaiwa.

In the midst of his run in wXw, in 2011, he took part in numerous shows with their main Japanese partner at the time, Big Japan Pro Wrestling.

In Yokohama, on 5 May, he teamed with Combat Zone Wrestling (CZW) owner D. J. Hyde to defeat Abdullah Kobayashi and Shadow WX.

He returned to Japan in April 2012, teaming with Sekimoto to defeat Yoshihito Sasaki and BJW Strong ace Yuji Okabayashi.

The first match of the tour for Walter, on 27 July, involved him and fellow wXw wrestlers Robert Dreissker and "Bad Bones" John Klinger losing to Okabayashi, Sekimoto and Sasaki.

On 30 July, he and Dreissker failed to win the wXw World Tag Team Championships, losing to the Sumerian Death Squad (Tommy End and Michael Dante).

In late 2019, it was announced that Walter would compete at BJW's Ryogokutan 2019 show, at the Ryōgoku Kokugikan, where he would team with Sekimoto to face Okabayashi and Yuji Hino.

Within this time, Walter began to form an alliance with the Sumerian Death Squad (Tommy End and Michael Dante) as "The Mind".

[25] Their first defense of the titles came at the Hasta La Victoria Siempre Tour Finale, where they would defeat the Sumerian Death Squad and the Leaders Of The New School (Zack Sabre Jr. and Marty Scurll).

In 2014, he changed his ringname to Big Daddy Walter, winning the his third Unified World Wrestling Championship on July after defeated Tommy End.

[30] He lost the title against Karsten Beck in January 2015, after 174 days as champion, in a match where Vince Russo appeared as the special referee and planned a screwjob against Walter.

After beating David Starr and Marius Al-Ani by referee's decision within two days, Walter vengefully defeated Matt Riddle before losing to Ilja Dragunov in the finals of the tournament.

Within 31 March and 6 June 2017, Walter failed to gain the Unified World Wrestling Championship thrice by losing to the incumbent champion, Jurn Simmons.

At Inner Circle 4 on 5 October 2017, amidst the World Tag Team League weekend, he defeated Thatcher in an "AMBITION rules" match.

They advanced in their block, defeated The Briscoe Brothers and EYFBO in the process, whilst losing to Homicide and Low Ki, They defeated David Starr and Jurn Simmons in the finals of the tournament, and, in the process, also won the wXw World Tag Team Championships, his third overall reign.On 15 October 2017, in Leipzig, Walter failed to win the Unified World Wrestling Championship again, this time in a no contest in a four-way match against incumbent champion John Klinger (who had become the biggest heel in the company with his faction RISE), Ilja Dragunov and Jurn Simmons.

Thatcher and Walter's first defense as World Tag Team Champions came on 3 November, defeating Bobby Gunns and Jaxon Stone.

On 23 December, at wXw's 17 Anniversary, Walter and Thatcher defeated Tarkan Aslan and his brother Lucky Kid in another successful defense.

[41] At the 16 Carat Gold 2018 weekend, Walter was scheduled to compete in a wXw Unified World Wrestling Championship match at the Saturday show against John Klinger.

[48] During the 2019 16 Carat Gold tournament between 8 and 10 March 2019, Walter lost in the finals to Lucky Kid after he defeated David Starr, Fenix and Avalanche in the previous stages.

He made his PWG debut during the 2017 Battle of Los Angeles tournament, where he was eliminated by eventual finalist Keith Lee in the opening round.

[67] Two months later, on 12 January 2019 at NXT UK TakeOver: Blackpool, Walter made his surprise debut by confronting WWE United Kingdom Champion Pete Dunne and attacking defeated challenger Joe Coffey.

[83] Prior to Gunther's title defense at Clash at the Castle on 3 September against Sheamus, Ludwig Kaiser announced the reformation of Imperium by reintroducing Fabian Aichner, now known as Giovanni Vinci.

[87] Gunther spent the remainder of 2022 and the early months of 2023 retaining the Intercontinental Championship against Rey Mysterio, Ricochet, Braun Strowman, and Madcap Moss in respective singles matches on various Smackdown episodes.

[93][94] In the coming months, Gunther successfully defended the Intercontinental Championship against Mustafa Ali at Night of Champions on 27 May, Matt Riddle at Money In The Bank on 1 July, and Drew McIntyre at SummerSlam on 5 August.

[101] At Night 1 of WrestleMania XL, Gunther was defeated by Sami Zayn for the Intercontinental Championship, ending his record-setting reign at 666 days and making it his first pinfall loss as part of WWE's main roster.

[105] In a rematch from King and Queen of the Ring, Gunther would defeat Randy Orton at Bash in Berlin on 31 August in his first title defence.

[108] At Survivor Series WarGames on 30 November, Gunther defeated Priest in a SummerSlam rematch to retain the title after interference from Finn Bálor.

[115] He owned a clothing brand alongside Marcel Barthel and Axel Tischer named Ringkampf Apparel from 2015 until 2020, which had numerous sponsored wrestlers including former Ringkampf stablemate Timothy Moura (who is best known as Timothy Thatcher), Raquel Lourenço (who is best known as Killer Kelly), former Imperium stablemate Fabian Aichner (now known as Giovanni Vinci), and Jeff Cobb.